Ernie wrote:

Is it normal for the battery gauge to read 16

If the 16 volts displayed is accurate it is a bit too high for
continuous charging of a lead acid battery, that is the "equalizing"
voltage. Check the charging voltage with a good quality voltmeter before
you start changing things because the cheap panel meters supplied with
consumer grade boats are not known for their accuracy.

If you have access to the battery while running and the battery is a wet
cell with removable cell covers (where you add water) look and see if
the cells are bubbling. If there are a lot of bubbles and/or you have
been adding a lot water then your charging voltage is probably high.

Rick